On Thu, Dec 15, 2022 at 11:27:19AM +0800, Jason Wang wrote:
> Commit a7766ef18b33("virtio_net: disable cb aggressively") enables
> virtqueue callback via the following statement:
>
> do {
> ......
> } while (use_napi && kick &&
> unlikely(!virtqueue_enable_cb_delayed(sq->vq)));
>
> When NAPI is used and kick is false, the callback won't be enabled
> here. And when the virtqueue is about to be full, the tx will be
> disabled, but we still don't enable tx interrupt which will cause a TX
> hang. This could be observed when using pktgen with burst enabled.
>
> Fixing this by trying to enable tx interrupt after we disable TX when
> we're not using napi or kick is false.
>
> Fixes: a7766ef18b33 ("virtio_net: disable cb aggressively")
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
> The patch is needed for -stable.
> Changes since V1:
> - enable tx interrupt after we disable tx
> ---
> drivers/net/virtio_net.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 86e52454b5b5..dcf3a536d78a 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1873,7 +1873,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
> */
> if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
> netif_stop_subqueue(dev, qnum);
> - if (!use_napi &&
> + if ((!use_napi || !kick) &&
> unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
> /* More just got used, free them then recheck. */
> free_old_xmit_skbs(sq, false);
This will work but the following lines are:
if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {
netif_start_subqueue(dev, qnum);
virtqueue_disable_cb(sq->vq);
}
and I thought we are supposed to keep callbacks enabled with napi?
One of the ideas of napi is to free on napi callback, not here
immediately.
I think it is easier to just do a separate branch here. Along the
lines of:
if (use_napi) {
if (unlikely(!virtqueue_enable_cb_delayed(sq->vq)))
virtqueue_napi_schedule(napi, vq);
} else {
... old code ...
}
also reduces chances of regressions on !napi (which is not well tested)
and keeps callbacks off while we free skbs.
No?
> --
> 2.25.1
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